\begin{problem}{Lights}{lights.in}{lights.out}{1 second}{32 megabytes}

$2N$ light bulbs are arranged in two rows and $N$ columns.
Each light bulb can be either off or on, and all lights are initially off.

We want to turn some of them on so that they form a beautiful pattern.
In one step we can change the state of a sequence of (one or more) consecutive
light bulbs in the same row or column.

Given the desired pattern, write a program that finds the minimal number of
steps required to form the pattern.

\InputFile

The first line of input contains an integer $N$ ($1 \le N \le 10,000$) --- the number of columns.

Each of the following two lines contains a sequence of $N$ characters representing the
desired final pattern. Character `\t1' indicates a light bulb that should be on in the
final state, while the character `\t0' indicates a light bulb that should be off.


\OutputFile

Output the minimal number of steps required.

\Example

\begin{example}
\exmp{
3
100
000
}{
1
}%
\exmp{
5
11011
11011
}{
3
}%
\exmp{
20
11101101111000101010
01111101100000010100
}{
7
}%
\end{example}

\end{problem}
